DT 300 - fail to start - TPS voltage value at 0 position ?

[Henry]

Looks pretty normal to me. I think there is a common power interruption possibility that would be sensed as turning the systems off and on. Something that would not be sensed as a fault, hence no code. Could also be a bad plug cap and/or plug wire. Also could go back to low voltage to the ECU while cranking. I know you measured really good voltage while trying to start measured at the battery. But what is the voltage AT the ECU?

You have been handed a toughie on this one! Two machines with the same symptoms but otherwise perfectly envious performance otherwise. Write down everything that has been ruled out. No dealer tech ANYWHERE would even be allowed to sort this out. Right now, YOU are the world's ranking true authority. Why? You are there, you have the analyzer tool (that most US dealers do not have), you have the motivation to solve because you actually use this mode of transport daily, you have the ability (demonstrated) potential and I will think up a couple more reasons soon!

We all will benefit from your discovery.

Thanks for your kind words  but I think I have no authority, otherwise I wouldn't come here to get advises concerning my problem ! (2 actually  )
I'm sure all dealers have the Fi diagnostic tool, otherwise how would they do to point a bad sensor for example ?? Whey charge for all of them ? That would be a massive fraud !
As you said I have the motivation, that is absolutely right ! I could buy another scooter, but if I can avoid, I will. Buying another Downtown would make me a used spare parts dealer !

Coil/cable/cap/spark plug are new, I don't believe that is the problem.
A faulty ECU could, but how to make sure ? I'm not willing to buy a new one to check. My dealer doesn't take new parts back and has no spare to test

Maybe the engine quality overall is involved ? I ride from 2 to 10 times a day, every day (for my job), short distances in town, from 5 to 15 minutes rides. Maybe this kind of usage kills the internals ? I took compression mesures on both scooters, both are at 10 bars (hot), repair manual says 12bars +/-2, but my compression tool maybe crap...  But then, if it can start when cold and parked outside at 2°C (35F) after a 2 sec cranking + little bit on the throttle, it should start easily when the engine is hot if engine compression was the problem !

I'm lost !

[Ruffus]

@Henry, as a far shot,
how about to try changing ECU from one to the other scoot. If it's easy possible, to see how the motor reacts.
I would rinse this MAP sensor with brake cleaner to be sure its free. Don't touch the inner part of this sensor. Drying with moderate pressured air.

Please make sure your intake system is 100% tight, clamps, o-rings, injector, etc.

[dr.jazz]

ECU value are great!

Just one info, when engine is hot do you have O2 voltage cycling from 0.1 to 0.9?

You dont need to clean or check any sensor, not any more, you have perfect value...trouble is something else!

Take of fuel pump and ecu relay check for corrosion, also if relay looks clear, change that two relay with high and low beam (those two works fine I assume).....then test hot start! Check manual for relay location, if you cant, I can post it!

Weird fact is you have 2 same issue with 2 scooters, there is possibility it is maybe, I said again maybe fuel problem. So after you check relay, you can try buy some fuel aditive for petrol engine. Im from Croatia and here is fuel very bad, so I can tell you from first hand, depends from gas station to gas station I can feel big difference when starting engine, and vibrations when I cruze at 5500rpm.

About battery voltage, yes It can make trouble with ECU, when cranking voltage drop to low and ECU goes crazy and can manifest in many ways. However you should have biggest voltage drop when you cold start at couple celsius.

We need check cople more thing before we conclude ECU problem.

[CROSSBOLT]

This is a shot in the dark BUT my 2013 was purchased in 2016 as new, old stock. Whatever fuel that was in it was from 2013! Very soon that old fuel turned up some "slime" that partially clogged the injector. Symptoms were hard start in that it did not start within two revolutions. There were falters and flame-outs. No codes.

The fuel cap had been vented as soon as it was home. Starting voltage checked was above 10.5 and charging output nominal, like yours.

Pulled the injector and inspected spray plate (darn holes are SO SMALL even under magnification!). Observed NO SPRAY during key on/self check/prime. Disconnected fuel hose from injector inlet and pushed it on the injector spray nozzle. Cycled key on/off many times and short cranks many times until about 1 cc collected in a bottle cap. There was some snot-lookin' stuff in the cap that was back-flushed out. Put everything back and it fired right up normally! Have not had a problem since!

[Henry]

@Henry, as a far shot,
how about to try changing ECU from one to the other scoot. If it's easy possible, to see how the motor reacts.
I would rinse this MAP sensor with brake cleaner to be sure its free. Don't touch the inner part of this sensor. Drying with moderate pressured air.

Please make sure your intake system is 100% tight, clamps, o-rings, injector, etc.

I'm not sure ECUs are the same, they have different part numbers, I checked on Kymco-parts.
I'll rince the map sensor with brake cleaner as you suggest

[Henry]

ECU value are great!

Just one info, when engine is hot do you have O2 voltage cycling from 0.1 to 0.9?

You dont need to clean or check any sensor, not any more, you have perfect value...trouble is something else!

Take of fuel pump and ecu relay check for corrosion, also if relay looks clear, change that two relay with high and low beam (those two works fine I assume).....then test hot start! Check manual for relay location, if you cant, I can post it!

Weird fact is you have 2 same issue with 2 scooters, there is possibility it is maybe, I said again maybe fuel problem. So after you check relay, you can try buy some fuel aditive for petrol engine. Im from Croatia and here is fuel very bad, so I can tell you from first hand, depends from gas station to gas station I can feel big difference when starting engine, and vibrations when I cruze at 5500rpm.

About battery voltage, yes It can make trouble with ECU, when cranking voltage drop to low and ECU goes crazy and can manifest in many ways. However you should have biggest voltage drop when you cold start at couple celsius.

We need check cople more thing before we conclude ECU problem.

I don't think the 02 voltage was cycling, or just a bit, I didn't see the value going higher than 0.08, I will check tomorrow ! Could be the issue ?
Fuel here in Brussels is very good quality, I feed both scooters with 98 from branded gas station (Total, Esso, Q8...)

I will also check the relays for corrosion, I never thought about that, that also could be an issue as my scooter stays outside, not covered at all. Humidity is high in Belgium.
On the 300 I had corrosion on the frame, I once cleaned the ground bolt that looked rusted, no change, but I didn't check the relays.

[Henry]

This is a shot in the dark BUT my 2013 was purchased in 2016 as new, old stock. Whatever fuel that was in it was from 2013! Very soon that old fuel turned up some "slime" that partially clogged the injector. Symptoms were hard start in that it did not start within two revolutions. There were falters and flame-outs. No codes.

The fuel cap had been vented as soon as it was home. Starting voltage checked was above 10.5 and charging output nominal, like yours.

Pulled the injector and inspected spray plate (darn holes are SO SMALL even under magnification!). Observed NO SPRAY during key on/self check/prime. Disconnected fuel hose from injector inlet and pushed it on the injector spray nozzle. Cycled key on/off many times and short cranks many times until about 1 cc collected in a bottle cap. There was some snot-lookin' stuff in the cap that was back-flushed out. Put everything back and it fired right up normally! Have not had a problem since!

I also have pops & bangs sometimes, when I crank for a few times then bang ! Or, when I stop accelerating at mid range, around 4k rpm, there is a bang, at the moment I let the throttle go back, that doesn't happen a lot, maybe once a week, but it happend.
I took the injector off and observed the spray pattern when turning the key on (without crancking), it seemed quite regular, I'll try to video that. I'll inspect the injector with a magnifier to make sure it is clean, and I'll try your reverse method to back flush it, I never though doing that but I will do it tomorrow for sure !

What do you mean by "The fuel cap had been vented" ? My question may sound weird but my english is far from perfect (I'm French  )

[CROSSBOLT]

I also have pops & bangs sometimes, when I crank for a few times then bang ! Or, when I stop accelerating at mid range, around 4k rpm, there is a bang, at the moment I let the throttle go back, that doesn't happen a lot, maybe once a week, but it happend.
I took the injector off and observed the spray pattern when turning the key on (without crancking), it seemed quite regular, I'll try to video that. I'll inspect the injector with a magnifier to make sure it is clean, and I'll try your reverse method to back flush it, I never though doing that but I will do it tomorrow for sure !

What do you mean by "The fuel cap had been vented" ? My question may sound weird but my english is far from perfect (I'm French  )

Your english certainly fooled me! Better than most of us yanks born here! Har, har!

The vent valves for nearly all two wheelers stick shut and starve the engine for fuel. Carburetor engines just quit and are a bear to relight. EFI idle surges and/or goes high and at road speed lose power. I have vented the gas cap on nearly all of our bikes since 2005 because of this sticking valve. Very small hole: #60 drill about right....

[Ruffus]

@Henry, even ECUs part numbers aren't the same, IF connectors fit each other, I would give it a go.

-if there would be an electronic fault, you would see a DTC on your diagnostic tool

-leaves us to more trivial options like open circuits on relais, contact failures on connectors, by-air somewhere in your intake channel (injector, o-rings, vacuum lines, intake manifold, etc)
-fuel delivery in general might cause such a behaviour too, so pls go over fuel lines/pressure again
-pls take the air filter completely out for testing

-a frailed/loose cable (ground?) somewhere, which reacts/causes after being warmed up
-corroded connectors down to this cableshoes within fuse box
- O2-sensor in your exhaust pipe has 4(four) cables, all intact and plugs free of corrosion
-handlebar switches corrosion of all kind
-burnt out connector between generator/regulator
-second air system pipes and hoses messed up/clogged/melted.

[dr.jazz]

@Henry, even ECUs part numbers aren't the same, IF connectors fit each other, I would give it a go.

He can try swap ECU only if DT350 is Euro 3, because Euro 4 have EVAP system, he mention DT350 is 4 years old, It should be Euro 4

-if there would be an electronic fault, you would see a DTC on your diagnostic tool

It is more complicated then "dtc will pop out". In 15 years ECU diagnostic I have encountered many illogical problems and I can tell you ECU self-diagnosis is unreliable...very much!

@Henry

You must have O2 voltage cycling on idle when engine is warm, also when you hit throttle you should have spike to 0.9, and zero when you leave throttle (fuel cut off).. pls play with that little bit and write results here! Maybe it is clue for something...

Ruffus write very good check list, you should follow that!
My DT also stay all the time outside and I have habit once in year spray non water proof connectors with contact cleaner just for prevention!

[Henry]

I checked quite a lot of things today


I checked O2 sensor voltage when the engine was hot and running, at idle the voltage doesn't change, 0.07V, but on throttle it goes from this value to 0.90V.
I tried to start without the fuel tank cap, no change.
I back washed the injector, clean petrol came out.
I measured fuel pressure : 2.9 bars. Should be 3 but my measuring device is a cheap one, so it could be 3 !
I took the fuel pump out to inspect, I have no clue if the filter is supposed to look like this




The tank looks clean



The fuel pump o-ring that seals in between the pump and the tank was very loose, I put it back cause I didn't have any spare but I will replace it asap.

I tried to start with the air box disconnected, no change, it starts, but hardly, as usual.

I unplugged almost everything I could see, no sign of corrosion into plugs.
I checked ECU relay, clean. I swapped it with low beam relay, no change.

I couldn't try to swap it with the 300 because I have to dismantle many body parts on both machines and I didn't have enough time to do so.

All air lines seemed normal, the throttle body is firmly in place, maybe I should take the throttle body manifold off to inspect ? It looks really sturdy, I don't see why the gasket would let air go into, otherwise it would be rough even after start, no?

I spend to much time on that "thing" 

[Ruffus]

@Henry, I still think it's somehow "by-air" related.

-intake manifold,
-vacuum tubes,
-manifold o-ring or gasket,
-false air caused by an worn out throttle axle,
-injector o-ring,
-hose-clamps pinch not tight,

- intake manifold test: out, spray inside with a little fuel, dust outside with baby powder or chalk dust, if there is a hair gap, it shows on powder.

Three more thoughts:
A) if you separete those 3-pronged plug between generator and regulator, did you see burn-signs on its plastic body?
If yes, could mean your regulator was overcharged and caused erratic in your ECU.
Q: did you change your regulator for a new one?

B) both battery cables OFF battery, hold them together for a minute or so, to discharge your ECUs diodes.

C) take a cable of appr. 10mm2 and connect your
battery MINUS with your motor GROUND close to its starter motor to have a 100% circuit.

[CROSSBOLT]

Your fuel filter is over half blocked by that black stuff! The filter is a white nylon-plastic-screen thingy. That black stuff is some kind of Martian snot that should not be there!

[Ruffus]

@CROSSBOLT, this looks to me like a pattern on a fabric.. those black thingys....reminds me of a babys stocking..

@Henry, maybe this link unravels something..
At chapter 13. is a ECU testing diagram....
-check the tilt switch too

https://www.google.com/url?sa=t&source=web&rct=j&url=http://kymco.at/pub/media/Download/Kymco/Downtown300iFehlercode.pdf&ved=2ahUKEwjT_PG6jeT0AhWTg_0HHaRTAJMQFnoECDQQAQ&usg=AOvVaw1NYgIIcBUDGUBOzA8Ouyh7

[CROSSBOLT]

@CROSSBOLT, this looks to me like a pattern on a fabric.. those black thingys....reminds me of a babys stocking..

@Henry, maybe this link unravels something..
At chapter 13. is a ECU testing diagram....
-check the tilt switch too

https://www.google.com/url?sa=t&source=web&rct=j&url=http://kymco.at/pub/media/Download/Kymco/Downtown300iFehlercode.pdf&ved=2ahUKEwjT_PG6jeT0AhWTg_0HHaRTAJMQFnoECDQQAQ&usg=AOvVaw1NYgIIcBUDGUBOzA8Ouyh7

Good point about the tilt switch! Could be a gremlin.

Stig found a replacement for his fuel pump at the Yamaha camp...for WAY less than the Kymco assembly....AND the filters on old and new (if memory serves..) were pristine white screen. Now, if that is for certain blocking flow I would think it would only bother at max speeds.